Stripping system for concrete slab casting form



Oct. 24, 1967 T. W. SHOE ing/ew.' l YMQW@ We EOBERTLKAHN United States Patent O 3,348,279 STPING SYSTEM FOR CONCRETE SLAB CASTING FORM Theodore W. Shoe, Troy, Ohio, assigner to The Flexicore Co., Inc., Dayton, Ohio, a corporation of New York Filed Oct. 21, 1965, Ser. No. 500,114 7 Claims. (Cl. 25-120) This invention relates to a stripping system for concrete slab casting form and is an improvement upon the means for stripping a concrete slab casting form as disclosed in United States Patent No. 3,061,904, granted Nov. 6, 1962.

The casting forms to which this invention pertains are generally of the type disclosed in said United States patent. These casting forms have a generally U shaped section and are adapted to be stripped by arching the casting form bottom. In said patent, there is disclosed contour plate means providing a curved surface over which the bottom of such a casting form can be arched to secure stripping Without overstressing the form. Briefly, the casting form stripping involves the application of force to channels on opposite sides of the casting form to cause the form bottom to conform to the curvature of the contour plate.

Stripping generally is accomplished by hydraulic jack means, an example of such means being disclosed in United States Patent No. 3,142,106, granted July 28, 1964. The forces generated for stripping are powerful and must be controlled to prevent excessive force being applied to the casting forms. While the various stripping means and methods disclosed in the above identified patents permit of a substantial margin of error insofar as the magnitudes of stripping forces are concerned, nevertheless it is desirable to provide means for monitoring the operation of the hydraulicmeans at the region where stripping forces are applied.

The invention hereinafter disclosed makes possible a simple and effective monitoring system whereby the stripping force applied to a casting form can be limited to that required for arching the bottom of the casting form over the prescribed surface of the contour plate. In general, the invention utilizes the relative positions of a casting form bottom and the arched contour surface for controlling the application of stripping force to the system. The stripping means disclosed in the prior patents referred to have utilized as a control factor, the magnitude of the force applied for stripping. This is generally satisfactory if the hydraulic system being used is controlled to apply a predetermined force for stripping and if the force is properly calibrated for the job. However, Where a number of different casting forms are to be stripped or the casting form characteristics change, it may be necessary to apply different stripping forces to prevent damage to the casting forms. In addition, the control equipment must be sensitive enough to respond t-o small variations in pressure in hydraulic systems.

Pressure responsive control means for hydraulic systems often develop faulty response characteristics and precise response of such control means cannot always be obtained. In the stripping systems disclosed in the above identified patents, a substantial increase in stripping force due to faulty response of controls may cause serious damage to expensive casting forms.

In its more general aspects, the invention contemplates providing one or more air escape passages or ducts at a contour plate and associated control means responsive to large changes in the air passage impedances for control action. The air ducts are located at portions of the contour plate which are normally adjacent to the contour plate edges, these, in turn, being adjacent to the sides of a casting form being stripped. The air ducts rely upon the ice bottom of a casting form being stripped to function as a valve element for substantially closing the air ducts at the contour plate surface when the casting form bottom is in proper position for stripping. The invention will now be described in conjunction with the drawing wherein FIG. l is a diagrammatic representation of a stripping system employing the invention. FIG. 2 is a detail illustrating a modification in part of the system, and FIG. 3 is an enlarged detail of an end of the duct.

A casting form generally indicated by l0 can be of the type disclosed in the first patent previously referred to. The exact structure of the casting form for use with the present invention is not important except that for stripping, bottom 12 of the casting form must be arched as illustrated to conform to the curvature of contour plate 14. Contour plate 14 is disclosed in the second patent previously identified. Casting form 10 has channels 15 and 16 on opposite sides thereof, these channels being used to obtain the stripping action. As more fully disclosed in said patents, stripping is accomplished by restraining the channels with hooks 17 and applying force to cause bottom 12 of the casting form to bow or arch about surface 18 of the contour plate. Normally, prior to the application of stripping force to channels 15 and 16, bottom 12 of the casting form is generally flat (see, for example, FIG. 7 of the second patent), and rests upon the crown or high part of contour plate 14. In the final stripping position, bottom 12 is arched so that it bears against substantially the entire transverse extent of surface 1S of the contour plate. This may be accomplished by pullingy down on the channels, or urging the contour plate up or both.

A simple means for accomplishing the stripping is illustrated. Contour plate structure 14 can be urged upwardly by hydraulic piston 14a working in hydraulic cylinder 14h. Cylinder 14b is coupled through hydraulic pressure control 14C to hydraulic pressure source 14d. It is understood that control 14e` is an automatic control to limit the amount of stripping force applied to urging contour plate structure upwardly. Control 14C can cause damage to the casting form if, for some reason, hydraulic pressure on piston 14a exceeds the value necessary for accomplishing the stripping.

In accordance with the present invention, contour plate structure 14, which may be one or a number of blocks of metal, is provided with air ducts 20 and 21 adjacent edges 23 and 24 of a contour plate. Air ducts 20 and 21 terminate at contour surface 18.

The dimensions of air ducts 20 and 21 insofar as cross section are concerned are not important except that once determined, these dimensions should remain substantially constant for various installations. This is to permit precalibrated controls to be used. However, it is desirable to avoid having to provide ducts 20 and 21 with fine toler ances. The contour plates are massive and thick and cann-ot be accurately drilled unless precautions are taken. It is preferred, therefore, to have air ducts 20 and 21 of substantial diameter such as, for example, about the order of 3716 and provide an orifice insert for each duct. Thus, inserts 20a and 21a are inserted into the top or contour face end of each duct. These inserts are of steel or any other suitable material and can be about 3/8 long and have a bore of the order of about 1/16. It is quite simple to manufacture such inserts to a tolerance of the order of about .001" or .002, both in regard to the diameter of the bore and length. Thus, an accurate insert may be provided for each duct. The free end of each insert is preferably disposed just a bit below the level of the contour surface to avoid the possibility of interference and damage when the bottom of the casting form comes down against the contour plate.

Connected between ducts and 21 and compressed air source 28 are adjustable throttle valves Z5 for providing a high resistance to substantial air ow.

Air pressure responsive means 26 and 27 are connected in the air lines adjacent air ducts 20 and 21. Compressed air at any desired air pressure such as about 30 or 40 lbs/sq. in. is usually available and can be used. Instead of throttle valves, capillary tubing 2S of suitable length may be used as illustrated in FIG. 2.

Each air pressure responsive means may be conventional and, as an example, may have expansible bellows 26a whose interior communicates with the air pipe line going to throttle valve Z5. Bellows 26a is associated with an adjustable spring loading means 2Gb and has electrical.- contacts 26C. Each air pressure control thus has anelectric switch which is open or closed, as the case may be, and which controls the condition of hydraulic pressure control 14C. The arrangement is such that in the event that air duct 20 or 21, or both of them, is substantially closed by the bottom of the casting form, the increased air pressure within bellows 2da changes the condition of switch C and actuates hydraulic pressure control 14C to prevent the application of further hydraulic pressure to the piston 14a.

During stripping, the casting form bottom approaches the free ends of air ducts 20 and 21 and in the final stripping position function to provide an air seal. Even though a perfect air seal may not be obtained, the reduction in air flow through ducts 20 and 21 and their orifices is so great that escape of air at the casting form bottom is practically cut of. This will result in a sharp jump in air pressure and permits such pressure changes to be used as an actuating means for controlling the power to the stripping means. Thus, when casting form bottom 12 reaches its final position over contour plate surface 18, the control action comes into play. By having the air ducts 20 and 21 close to the contour edges, the control action is delayed until full stripping position is reached. By locating the air ducts further from the edges, the control action may be initiated earlier. The control of the stripping means is thus determined by the position of the casting form bottom rather than by the magnitude of the stripping force. It Will be understood that the control is for the purpose of preventing any increase in the stripping force magnitude beyond that required for stripping. After the casting form is in p0- sition for stripping, the form must be retained in such position to permit actual removal of thecasting. The stripping condition may be maintained by keeping the hydraulic pressure of the stripping means constant or by mechanical means for retaining the form in stripping position (as by hooks, etc.) After stripping has occurred, the form is released and permitted tostraighten out.V

The air control ducts may be provided at intervals along the length of an entire stripping system.

While compressed air is preferred, suction may be used to reverse the air ow. Compressed air is preferred and not only keeps the passages clean but can provide a much greater pressure differential for operation.`

The control over hydraulic jacks by pressure responsive means 26 may be exercised in a number of ways. Thus, one or more controls 26 alone may be used to shut off power or two operate in series relation as by connecting switches in series. The control action of pressure responsive means 26 can be applied to hydraulic pressure control 14C to hold the hydraulic pressure fixed and prevent increase in hydraulic pressure or to cut-off the pressure for a short time (as a second or two) land then re-apply the same pressure. In general, the air pressure control can be set to operate and cut-oif stripvping action only after the predetermined setting of automatic control14c has failed to act, or can be used as a primary control Without regard to automatic control 14C.

In connection with the pipe between throttle valve 25 and ducts 20 and 21, While considerable latitude in the pipe diameter is possible, it is desirable to observe the following: If the pipe connections are too small in diameter in comparison to the rest of the system, the fluid fow resistance may be great enough to create an undesired back pressure and reduce the sensitivity of the system. For example, diameters of about Vs" to 1A" are satisfactory. On the other hand, if the pipes are too large in diameter or too long in length, the pipes will act as a fluid reservoir and create an undesirable time delay before the air pressure control will function. This, of course, is a consideration in theV overall engineering of a system embodying the present invention. It is clear that the response characteristics of the hydraulic pressure control 14C as well as the size of bellows 26a will -also have to be considered.

lnV general, the determination of the pipe connections is simple and, as a rule, not critical within a substantial range of Values.

What is claimed is:

1. In a system for stripping casting forms having normally fiat bottoms, said system having contour plate means to define a curved surface over which a casting form bottom is arched to conform to said curved surface and power means are provided for arching the casting form bottom, the improvement comprising air duct means having a free air discharge end lying generally in the curved surface defined by the contour plate means, means including a connection between said air duct means and a source of compressed air and normally providing substantial air ow resistance to said air duct means, said free duct end being Vadapted to be substantially closed as the bottom of said casting form approaches the desired arch stripping shape and means responsive to the rise in air pressure incident to the substantial blockage of air discharge from the normally free duct end for controlling the power means for arching the casting form bottom.

2. The system according to claim 1 wherein said connection between said air duct means and source of compressed air comprises a throttle valve.

3. The system according to claim 2 wherein said air duct means includes an orifice for said air duct, said orifice being located to provide a termination for said air duct.

4. The system according to claim 3 wherein said orifice terminates just below the contour plate surface.

5. The system according to claim 1 wherein said counection between said air duct means and source of compressed air comprises capillary tubing,

6. The system according to claim 1 wherein said power means for arcing the casting form bottom includes means energized by hydraulic pressure and control means responsize to the hydraulic pressure to provide a hydraulic power system, said means responsive to the change in air pressure controlling said hydraulic system for monitoring the operation of said hydraulic system to insure that said casting form is not overstressed after reaching its stripping position.

7. The system according to claim 1 wherein the piping between the ducts at the contour plate means and the air responsive means is selected so that the overall response characteristics are not deleteriously aiected with regard to sensitivity on the one hand and speed of response on the other hand.

References Cited UNITED STATES PATENTS 3,023,477 3/1962 Smith et al 25--120 XR 3,061,904 ll/l962 Wise 25-120 3,142,106 7/1964 Wise et al 25-120 3,305,909 2/ 1967 Wise et a1. 249-66 XR WILLIAM I. STEPHENSON, Primary Examiner. 

1. IN A SYSTEM FOR STRIPPING CASTING FORMS HAVING NORMALLY FLAT BOTTOMS, SAID SYSTEM HAVING CONTOUR PLATE MEANS TO DEFINE A CURVED SURFACE OVER WHICH A CASTING FORM BOTTOM IS ARCHED TO CONFORM TO SAID CURVED SURFACE AND POWER MEANS ARE PROVIDED FOR ARCHING THE CASTING FORM BOTTOM, THE IMPROVEMENT COMPRISING AIR DUCT MEANS HAVING A FREE AIR DISCHARGE END LYING GENERALLY IN THE CURVED SURFACE DEFINED BY THE CONTOUR PLATE MEANS, MEANS INCLUDING A CONNECTION BETWEEN SAID AIR DUCT MEANS AND A SOURCE OF COMPRESSED AIR AND NORMALLY PROVIDING SUBSTANTIAL AIR FLOW RESISTANCE TO SAID AIR DUCT MEANS, SAID FREE DUCT END BEING ADAPTED TO BE SUBSTANTIALLY CLOSED AS THE BOTTOM OF SAID CASTING FORM APPROACHES THE DESIRED ARCH STRIPPING SHAPE AND MEANS RESPONSIVE TO THE RISE IN THE AIR PRESSURE INCIDENT TO THE SUBSTANTIAL BLOCKAGE OF AIR DISCHARGE FROM THE NORMALLY FREE DUCT END FOR CONTROLLING THE POWER MEANS FOR ARCHING THE CASTING FORM BOTTOM. 